Moisture detector

ABSTRACT

A detector unit ( 1 ) which, in the presence of moisture, operates a remote alarm via a wire-less link is contained within a sealed liquid-impermeable housing ( 2 ). The unit is powered by electrical charge stored in a capacitor, which may be rapidly recharged by inductive coupling. Remote sensing electrodes ( 69, 70 ) are formed by depositing an electrically conductive ink onto a disposable moisture-absorbent tail ( 65 ).

TECHNICAL FIELD OF THE INVENTION

This invention relates to a moisture detector, particularly, but notexclusively, for detecting urine.

BACKGROUND

It is already known, e.g. from GB 2 219 679 A, to use a battery-operatedmoisture detector in a babies nappy (diaper). When the nappy becomes weta radio signal is sent to a remote indicator which generates an audiblesignal to indicate that the nappy requires changing.

The present invention seeks to provide a new and inventive form ofmoisture detector.

SUMMARY OF THE INVENTION

The present invention proposes a moisture detector comprising a detectorunit which is arranged to operate a remote alarm via a wire-less linkwhen moisture is present, in which the detector unit is powered byelectrical charge stored in capacitor means.

The capacitor means may comprise a single capacitor or a bank ofcapacitors.

In a preferred form the detector unit comprises a sealedliquid-impermeable housing containing said capacitor means, and anexternal moisture sensor.

The moisture sensor preferably comprises a pair of moisture-sensingelectrodes. In a preferred form of the device the moisture-sensingelectrodes are remote from the housing of the detector unit. Theelectrodes are preferably incorporated in a moisture-absorbent tail andare preferably formed by depositing an electrically-conductive ink ontoa flexible moisture-absorbent strip.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred totherein are included by way of non-limiting example in order toillustrate how the invention may be put into practice. In the drawings:

FIG. 1 is a general view of a detector unit of a moisture detector inaccordance with the invention;

FIG. 2 is a block circuit diagram of the detector unit;

FIG. 3 is a general view of a receiver unit of the moisture detector;

FIG. 4 is a block circuit diagram of the receiver unit;

FIG. 5 is a general view of a charger unit for use with the detectorunit;

FIG. 6 is a general view of a modified form of the detector unit;

FIG. 7 is a general view of further modified form of the detector unit;and

FIG. 8 is a more detailed view of the detector unit of FIG. 7.

DETAILED DESCRIPTION OF THE DRAWINGS

The equipment comprises three separate units, namely a detector unit(FIG. 1) to be placed in a babies nappy, a receiver unit (FIG. 3)carried by an adult (normally the babies mother), and a charger unit(FIG. 5) for re-charging the detector unit as necessary.

Referring to FIG. 1, the detector unit 1 has a soft encapsulating sealedmoisture-proof outer case 2 of a soft and flexible material such aslatex rubber, silicone rubber or plastic, which encloses the electroniccircuitry to prevent contact With urine. The electronics are furtherencapsulated in resin within the case 2 to provide mechanicalprotection. Two electrodes 3 and 4 of corrosion-resistant metal areexposed on the external surface of the case 2, which serve a dualfunction of moisture sensors and providing contacts via which thedetector unit can be re-charged. When placed in the nappy the sensorelectrodes are placed in contact the moisture-absorbent material of thenappy, but preferably not in contact with the babies skin to preventnormal skin moisture from triggering the unit. In any event it ispreferable to set the detection threshold such that the unit is nottriggered by normal skin contact.

Referring to FIG. 2, the electronics is powered from a rechargeablecapacitor 10 comprising thin conductive layers separated by a thin layerof an electrical insulating material. A tantalum or electrolyticcapacitor may be used, e.g. of wet type double layer electrolyticconstruction, having a value from serval thousand microfarads up toseveral farads. A detector circuit 11 monitors the electrical impedancebetween the electrodes 3 and 4 and signals a microprocessor-based codegenerator 12 when the impedance falls below a predetermined thresholddue to presence of moisture. Upon receiving the signal from the detector11 the generator 12 activates a high frequency radio transmitter 13which transmits the code by frequency modulation via an aerial 14, alsoenclosed within the case 2.

The detector 11, generator 12 and transmitter 14 employ CMOS technologyso that the circuit is of a high supply impedance and therefore draws avery low current from the capacitor 10. By using high impedanceelectronics the current consumption can be reduced sufficiently to allowthe device to operate for more than an hour without recharging. Thetransmitter 14 only generates a few microwatts of radio frequency power,but this is sufficient to be detected over a distance of about 50metres. The use of a capacitor has several advantages. Firstly, iteliminates corrosive and/or toxic substances which are widely used inbatteries. Secondly, a capacitor does not suffer from memory problemsassociated with the use of rechargeable batteries which reduces theirstorage capacity, so that the service life of the unit is considerablyincreased. Thirdly, a capacitor can be fully charged in a matter ofseconds, much less than the time normally taken to change a nappy. Theunit can therefore be used without interruption and no battery changingis necessary.

The capacitor power source 10 is provided with a charge monitor circuitwhich signals the microprocessor 12 when the capacitor voltage fallsbelow a predetermined level. The microprocessor then generates adifferent code which is transmitted by the unit 13 to signal that thedetector unit requires recharging.

Referring to FIG. 3, the portable receiver unit 20 incorporates anon/off switch 21 and a receiving aerial 22, which although shownexternally will normally be internal to the case 23. The unit may beprovided with a mounting clip (not shown) and houses a radio receiver 30as shown in FIG. 4. The receiver unit electronics are powered from aconventional battery supply 31 so that there is no need for frequentrecharging. Upon receiving a signal from the detector unit 1 amicroprocessor-based code detector 32 interprets the code and operatesan alarm device 33 to signal either that the nappy is wet or that thedetector charge is low. Different coloured LEDs could be used toindicate the two different alarm conditions. Both states are signalledto the mother by a beeper that continues to sound until the receiverunit is switched off.

When removed from the nappy the detector unit 1 may be recharged byplacing the electrodes 3 and 4 against two contacts 40 and 41 of amains-powered charging unit 42, shown in FIG. 5. The detector may beheld in a cradle, rather like a mobile phone charger. When the detectorunit draws current to recharge the capacitor 10 an LED 43 on the chargerunit illuminates to confirm that a good electrical contact exists. Thecapacitor may be arranged to receive power via a rectifier so thatshould the detector unit be connected the wrong way round no harm willresult, but the capacitor will not charge and the LED will notilluminate. After about 30 seconds, when the capacitor reaches fullcharge (about 5 volts), the LED fades to indicate that the detector isready for use.

A preferred arrangement is to charge the capacitor by inductive couplingwith the charger whereby an alternating current is induced in anelectromagnetic coil 80 within the housing 2 (FIG. 2) and is rectifiedby diode 81 to charge the capacitor 10. This eliminates the need for aphysical connection with the charger. Again, charging is very rapid.

The detector unit 1 should be wiped clean with a damp cloth or tissuebefore being re-used.

The modified detector unit 1 shown in FIG. 6 again has a softencapsulating sealed moisture-proof outer case 2 which encloses theelectronic circuitry. However, the electrodes 3 and 4 are replaced by atwo-pin connector 50 to which a mating connector 51 can be attached. Theconnector 51 is joined by a twin insulated wire 52 to a remote moisturesensor 53 which, by way of example, could comprise a pair of closelydisposed tracks carried on the surface of an insulating plate. This formof the detector unit 1 can be mounted outside the nappy within thebabies clothing or tucked inside the waist band of the nappy. The sensor53 is inserted into the nappy in contact with the moisture-absorbingmaterial so that when the nappy becomes wet with urine a signal is sentto the electronics to trigger an alarm as described above. However theremote sensor has the advantage that the unit 1 is not in direct contactwith urine and therefore requires less frequent cleaning. The sensor 53is simply uncoupled at the connectors 50/51 and sterilised or discarded.

The capacitor power source within the unit 1 can be recharged via theconnector 50 or preferably by inductive coupling as described above.

For cosmetic reasons it is desirable to incorporate the wires 52 into aflexible tape, sleeve or nappy liner which is discarded along with theconnector 51 and sensor 53. Furthermore, the sensor 53, wires 52 andconnector 51 could be integrally incorporated into a disposable nappy sothat they are discarded along with the nappy, the unit 1 still being areusable item. The detector unit which is shown in FIGS. 7 and 8 allowsthis to be achieved in an inexpensive but very effective manner. Theunit 1 again includes a soft moisture-proof case 2 which encloses theelectronic circuitry. In place of the two-pin connector 50 there are twoelectrical contacts 60 mounted on opposite sides of the case 2. The unit1 is inserted into a disposable pocket 61 which has an integral sensingtail 62.

The pocket 61 and tail 62 are formed from a strip 65 of strongmoisture-absorbent tissue paper like material having enlarged areas 63and 64 at opposite ends to form the pocket 61. On one side only of thesheet an electrically-conductive layer is deposited by a printingprocess using an electrically-conductive carbon-containing ink. Acontact area 67, 68 is deposited in the centre of each area 63 and 64with respective conductive tracks 69 and 70 which end mid-way along thestrip. The tracks 69 and 70 are not mutually joined and are offsettowards opposite edges of the strip so that when the strip is foldedalong a centre line 71 the two tracks still do not make electricalcontact along the tail 62. The two superimposed halves of the strip 65are secured together by an adhesive 73 which extends along the strip andaround the periphery of each end area 63, 64. However, the top of thepocket 61 remains open so that the detector unit 1 can be inserted,whereupon the contacts 60 make electrical contact with the conductiveareas 67 and 68. In order to retain the detector unit in the pocket 61 aflap 76 can be formed by an extended part of the enlarged area 64, whichmay be folded over and secured to the outer surface of the area 63 bymeans of a pressure-sensitive adhesive 77. The adhesive 77 canconveniently be protected by a peelable backing sheet (not shown) priorto use.

The pocket 61 containing the detector unit can be mounted outside thenappy within the babies clothing or tucked inside the waist band of thenappy. The sensing tail 62 is inserted into the nappy so that when thetissue-paper-like material becomes wet with urine the electricalresistance between the tracks 68 and 69 is reduced and a signal is sentto the electronics to trigger an alarm, as already described. After thealarm has been triggered the case 2 is removed from the pocket 61 whichis discarded with the attached sensing tail 62. The case 2 can berecharged and sterilised if necessary and replaced into a fresh pocket61 for re-use.

Although the above description refers specifically to use in a babiesnappy the moisture detector has a wider application. For example, thedetector could be used by incontinent adults or bed wetters. Similarly,the detector unit can be used to sense other kinds of moisture otherthan urine.

It will be appreciated that the features disclosed herein may be presentin any feasible combination. Whilst the above description lays emphasison those areas which, in combination, are believed to be new, protectionis claimed for any inventive combination of the features disclosedherein.

What is claimed is:
 1. A moisture detector which includes: a detectorunit (1) having a liquid-impermeable housing (2); moisture-sensing means(3, 4; 53; 65) which has a pair of moisture-sensing electrodes (3, 4;69, 70); a remote alarm (20) which is operable by the detector unit viaa wire-less link when moisture is present at the moisture-sensingelectrodes; and a charging unit (42) for receiving the detector unit tosupply electrical charge to the capacitor means, said detector unit (1)including capacitor means (10) for storing electrical charge to powerthe detector unit, and said charging unit being separate from saiddetector unit and said moisture-sensing means.
 2. A moisture detectoraccording to claim 1, in which the moisture-sensing electrodes comprisean electrically-conductive ink (69, 70) deposited on a flexiblemoisture-absorbent strip (65).
 3. A moisture detector according to claim2, in which the moisture-absorbent strip comprises two opposedmoisture-absorbent layers with ink deposited on mutually-opposed facesof the two layers.
 4. A moisture detector according to claim 3, in whichthe two layers form a pocket (61) for receiving the detector unit.
 5. Amoisture detector according to claim 4, in which the detector unit iselectrically connected with the moisture-sensing electrodes via areas ofelectrically conductive ink (67, 68) deposited on the inside of thepocket.
 6. A moisture detector according to claim 1, in which thedetector unit and the charging unit include inductive coupling means(80) for supplying electrical charge to the capacitor means.
 7. Amoisture detector which includes: a detector unit (1) having aliquid-impermeable housing (2); moisture-sensing means (3, 4; 53; 65)for attachment to the detector unit and which has a pair ofmoisture-sensing electrodes (3, 4; 69, 70) for location remote from thedetector unit; and a remote alarm (20) which is operable by the detectorunit via a wire-less link when moisture is present at themoisture-sensing electrodes; characterised in that the detector unit (1)includes capacitor means (10) for storing electrical charge to power thedetector unit when attached to the moisture-sensing means, and acharging unit (42) is provided for receiving the detector unit to supplyelectrical charge to the capacitor means (10), said moisture-sensingelectrodes comprising an electrically-conductive ink (69, 70) depositedon a flexible moisture-absorbent strip (65) comprised of two opposedmoisture-absorbent layers with ink deposited on mutually-opposed facesof the two layers, said layers forming a pocket for receiving thedetector unit, and said detector unit being electrically connected tothe moisture-sensing electrodes via areas of electrically conductive ink(67, 68) deposited on the inside of the said pocket.
 8. A moisturedetector according to claim 7, in which the moisture-absorbent stripcomprises a single length of moisture-absorbent material which is folded